In the investigation of earth formations for oil or other hydrocarbons, it is often advantageous to verify mineral composites, porosity and permeability of obtaining samples of the formation from the sidewall of a borehole drilled vertically therethrough. A borehole drilled for oil exploration, however, is usually only a few inches in diameter. BEcause of this size constraint, coring into the sidewall in a perpendicular direction and storing a number of cores is problematical. prior art coring devices have been unable to accomplish both perpendicular coring and storage of an appreciable number of cores, or have been incapable of drilling samples from hard materials in a formation. In addition, the horizontal depth of drilling has been limited by the dimensional constraints which a coring tool must meet.
The typical coring tool includes a drill bit driven by a coring motor. U.S. Pat. No. 4,354,558 issued on Oct. 19, 1982, to Jageler et al discloses a particular design for a coring tool in which the drill bit and coring motor are rotate into an operable position. But, this embodiment of the device taught in this patent cannot drill in a direction perpendicular to the sidewall. This reduces the usefulness of the core sample for analysis, and also reduces the perpendicular distance into the formation from which sample material can be taken. This tool is further limited in the small number of cores which it can store. Core sample storage is an important consideration since a tool with inadequate storage provisions will necessitate several trips down the borehold to obtain the required number of core samples. Such extra trips creates considerable expense, both directly and through lost rig time.
A need has thus arisen for a coring device capable of cutting samples from hard rock in an efficient and reliable manner. Such a device should cut into the sidewall of a borehole in a perpendicular direction to the greatest depth possible, and be capable of storing a large number of cores.